A prerequisite for a obtaining a high quality of such color patterns, e.g. when producing color video display screens, is a high uniformity of pixel density across the entire receiver plate. Apart from this macro-uniformity behavior, uniformity of optical density of the individual pixel elements and their crisp pixel edges are important parameters to increase the resolution of the color patterns produced. Uniformity and edge crispness of the transferred pixels is reached by substantially homogeneous light distribution and the impingement of parallel radiation, perpendicular through a mask, onto the receiver element, that is to say by uniform distribution of irradiance and perpendicular light incidence.
From DE-OS 23 47 287 and EP-PS 0 101 014 electronic flash devices are known whose reflectors are designed such that a variation of the light emitting angle and a uniform illumination of the receiver surface are possible.
CH-PS 636 714 discloses an electrostatic copier having a flash lamp whose reflector distributes the radiation of the lamp as uniform as possible onto a surface to be fused, thereby heating toner powder to melt.
A copier described in DE-OS 25 11 423 discloses a quartz iodine lamp which is arranged in one of the focal axes of an elliptic cylinder-shaped reflector. The opposite focal axis of the reflector is to coincide as exactly as possible with the surface of an image carrier and the toner layer coated thereon so that the toner layer is fused due to the radiant energy absorbed.
A disadvantage of the above mentioned arrangements is that neither a parallel nor a perpendicular light incidence onto the predetermined receiver at a transfer plane is obtained. Moreover, no high-energy light flash having a high radiant output can be produced on a relatively large receiver surface corresponding, for example, to a medium-sized video display screen.